1. Field of the Invention
The present invention relates to a liquid-phase growth process of immersing a base substrate in a heated solution containing reactant species to be grown dissolved therein and gradually cooling said solution to epitaxially grow said reactant species on said substrate and an apparatus suitable for practicing said liquid-phase growth process.
2. Related Background Art
It is known that when the solvent of a solution used for liquid-phase epitaxy is vaporized to deposit on a substrate before said substrate is immersed in said solution, an adverse effect is affected on liquid-phase epitaxial growth on said substrate.
Japanese Laid-open Patent Publication No. 5(1993)-330983 (Kumatoriya et al.) describes such adverse effect and a method for preventing said adverse effect from being brought about. Particularly, Kumatoriya et al. describes that in the case where a magnetic garnet single crystal film is grown on a base substrate by way of liquid-phase epitaxial growth from a solution comprising a solvent comprising PbO and B2O3 in which garnet constituent elements are dissolved, by making said solution to be in a supercooled state and immersing said substrate in said solution, there will be occurred a problem in that before the substrate is immersed in the solution, the substrate is directly exposed to vapor of PbO and the like vaporized from the solution where precipitates chiefly of PbO and the like are deposited on the substrate and this exerts an adverse effect which make it difficult to grow a high quality single crystal film on the substrate. Kumatoriya et al. describes a method for preventing this problem from being occurred in that a pair of baffle plates for preventing vapor of PbO and droplet of PbO from being deposited on the substrate are provided at a position above the substrate and at a position below the substrate.
However, the method of Kumatoriya et al. is still problematic in that because the baffle plates are retained on a substrate holder together with the substrate, it is difficult to prevent the solvent vapor from going around to reach the substrate. In addition to this, there is also a problem such that when the substrate is kept in a stand-by condition without being situated in the growth chamber, the solvent is vaporized to deposit on the inner wall face of the growth chamber so as to become a source which absorbs water and the like, where such source is liable to affect an adverse effect to the growth of the crystal film on the substrate. In addition, the method of Kumatoriya et al. has a disadvantage such that as the solvent is vaporized, a new solvent is necessitated to be suitably supplemented and this invites an increase in the production cost and a decrease in the productivity of a product.
Besides, in the case where an element whose melting point is low such as Ga is used as a solvent or a solute when a semiconductor crystal film is grown in accordance with the method of Kumatoriya et al., when the substrate is kept in a stand-by condition without being situated in the growth chamber, such element whose melting point is low is rapidly vaporized, where it is difficult to make the semiconductor crystal film to be grown on the substrate such that the composition of the semiconductor crystal film is uniform in every batch or the semiconductor crystal film is uniformly doped in every batch.
Separately, Weber et al., Appl. Phys. Lett. 66(10), pp. 1243-1245 (1995) describes that in the case where a silicon single crystal film is epitaxially grown on a base substrate from an indium solution, there is a problem such that prior to the step of immersing said substrate in said indium solution, said indium solution is liable to vaporize to deposit indium on the surface of the substrate, where said indium deposited on the substrate acts as a catalyst in such a way that oxygen and silicon in the atmosphere are reacted with each other to form a silicon oxide film on the substrate.
Similarly, there is known a technique in that in the case where a silicon single crystal film is epitaxially grown on a base substrate from an indium solution, a silicon substrate obtained by forming a porous layer on a surface of a silicon wafer and subjecting said silicon wafer to a hydrogen annealing treatment to flatten the surface thereof is used as said substrate. However, there is a problem in this case such that when prior to the step of immersing said substrate in said indium solution, said indium solution may evaporate to deposit indium on the surface of the substrate, where the flattened layer of the porous surface of the substrate is resorped due to the deposited indium such that the porous layer is exposed to bring about a growth defect in the structure of said silicon single crystal film grown on the substrate.